Loss-of-function mutations of the parkin gene, which encodes a ubiquitin-protein ligase, are a major cause of early-onset Parkinson's disease, and increasing evidence suggests that parkin dysfunction may also play a role in late-onset typical Parkinson's disease. To explore the biological role of parkin, and the mechanism by which loss of parkin function results in neurodegeneration, we recently created a Drosophila model of Parkinson's disease through mutational inactivation of a highly-conserved Drosophila parkin ortholog. Drosophila parkin mutants are semi-viable and display a late developmental defect in spermatid formation, widespread apoptotic degeneration of flight muscle, and degeneration of a subset of dopamine neurons in the central nervous system. Mitochondrial pathology is a prominent and early characteristic of tissue degeneration in parkin mutants and a significant fraction of Parkin localizes to mitochondria. From these findings we hypothesize that Parkin promotes mitochondrial integrity by directly ubiquitinating particular mitochondrial targets. To identify the substrates of Parkin that mediate mitochondrial and tissue integrity we propose to use in vivo proteomic approaches to identify Parkin-binding components and proteins displaying reduced ubiquitination in parkin mutants. An advantage of using Drosophila for these studies is that findings from our proteomic studies can be rapidly validated in tissues that require Parkin for viability, including dopamine neurons. This work should clarify the biological role of Parkin and will serve as a foundation for future hypothesis-driven investigation of parkin pathogenesis. [unreadable] [unreadable]